The present invention relates to a method of detecting a leak in a well tubular of a well. The well comprises a borehole lined with a well tubular that is cemented into the borehole. The well can be a fluid-producing well or an injecting well.
It is often difficult to detect the presence of a leak in the well tubular, and it is even more difficult to determine the location of such a leak.
It is an object of the present invention to provide a simple method to overcome this problem.
In accordance with the invention there is provided a method of detecting a leak in a well tubular of a well for the production of hydrocarbon fluid from an earth formation, the method comprising the steps of:
a) passing a sonic tool provided with a transducer package capable of sending an receiving a sonic signal, through the well tubular;
b) prior to start of hydrocarbon fluid production through the well, inducing the transducer package to transmit the sonic signal through the well tubular and to receive a reflected signal, and making a primary registration of the reflected signal indicative of a leak-free well tubular;
c) after start of hydrocarbon fluid production through the well, inducing the transducer package to transmit the sonic signal through the well tubular and to receive a reflected signal, and making a secondary registration of the reflected signal indicative of an operational well tubular;
d) comparing the primary and secondary registrations and detecting a leak in the well tubular from a difference between said registrations.
It is thus achieved that the primary registration serves as a reference which represents the situation of no leakage of fluids through the tubular. Any difference between the later registration and the reference provides an indication of the occurrence leakage through the well tubular.
Reference is made to U.S. Pat. No. 5,031,467. This publication discloses a method of detecting fluid flow behind the casing that can be used in the method of the present invention. Suitably, the transducer package is packed in set of pads which are in contact with the inner surface of the well tubular.